Manufacturing method of semiconductor device

ABSTRACT

Island-like semiconductor films and markers are formed prior to laser irradiation. Markers are used as positional references so as not to perform laser irradiation all over the semiconductor within a substrate surface, but to perform a minimum crystallization on at least indispensable portion. Since the time required for laser crystallization can be reduced, it is possible to increase the substrate processing speed. By applying the above-described constitution to a conventional SLS method, a means for solving such problem in the conventional SLS method that the substrate processing efficiency is insufficient, is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method of semiconductordevice having thin film transistor, particularly to a technique forforming crystalline semiconductor film, which comprises active layer ofthin film transistor.

2. Related Art

As a forming method of active layer on thin film transistor (Thin FilmTransistor: hereinafter, referred to as TFT), a technique, in which anamorphous semiconductor film is formed on a substrate having aninsulation surface, and then, crystallize the same in a manner of laserannealing or heat annealing, has been developed.

The laser annealing is known as a crystallization technique, in which ahigh energy is given to an amorphous semiconductor film only withoutallowing the temperature of a glass substrate to rise too high, andthereby, the amorphous semiconductor film is crystallized. Particularly,excimer laser is a typical laser, which oscillates short-wave lengthlight of 400 nm or less in wavelength, has been used since the laserannealing was developed. The laser annealing is carried out in such amanner that a laser beam is processed by means of an optical system soas to be shaped into a spot-like form or a linear form at a surface tobe irradiated, and the surface to be irradiated on the substrate isscanned by the processed laser beam; i.e., irradiation position of thelaser beam is shifted with respect to the surface to be irradiated.

However, the crystalline semiconductor film, which is prepared by meansof the laser annealing, comprises an aggregate of a plurality of crystalgrain (ordinary crystal grain size, which is prepared by means of aconventional excimer laser crystallization, is approximately 0.1-0.5μm), and, the position and the size of the crystal grain are not even.

As for the TFT, which is prepared on a glass substrate, in order toisolate elements, since the crystalline semiconductor film is formedbeing separated into island-like patterns, it was impossible to formcrystal grains at specified positions and sizes. Accordingly, it wasalmost impossible to form channel-forming areas with a monocrystalsemiconductor while eliminating the influences of the crystal grainboundary.

The interface (crystal grain boundary) of the crystal grain is an areawhere the translational symmetry of the crystal is decayed. It is knownthat, due to the influence of the recombination center or trappingcenter of the carrier, or the influence of the potential barrier in thecrystal grain boundary caused from the crystal defect or the like, thecurrent transport characteristics of the carrier is decreased, and as aresult, the OFF-current increases in the TFT.

A technique called as super lateral growth, by which, compared to thecrystal grain size via conventional excimer laser crystallization, alarger grain size can be formed, is known. A detailed description of thetechnique is disclosed in “On the super lateral growth phenomenonobserved in excimer laser-induced crystallization of thin Si films,James S. Im. and H. J. Kim, Appl. Phys. Lett. 64(17), Apr. 25, 1996,pp2303-2305”.

In the super lateral growth, a portion, where the semiconductor ismelted completely due to the irradiation of a laser beam, and a portionwhere the solid-phase semiconductor area remains, are formed, and then,the crystal growth begins around the solid-phase semiconductor area asthe crystal nucleus. Since it takes a certain period of time fornucleation to take place in the completely melted area, during theperiod of time until the nucleation takes place in the completely meltedarea, the crystal grows around the above-described solid-phasesemiconductor area as the crystal nucleus in the horizontal direction(hereinafter, referred to as lateral direction) with respect to the filmsurface of the above-described semiconductor. Therefore, the crystalgrain grows up to a length as long as several tens of times of the filmthickness. For example, with respect to the silicon film thickness of 60nm, a lateral crystal growth of 1 μm-2 μm in length takes place.Hereinafter, the phenomenon will be referred to as super lateral growth.

In the case of the above-described super lateral growth, although arelatively large crystal grain can be obtained, the energy intensityarea of the laser beam, where the super lateral growth is obtained, ismuch stronger than the intensity that is used in ordinary excimer lasercrystallization. Also, the range of the energy intensity area isextremely narrow. From the viewpoint of the position control of thecrystal grain, it is impossible to control the position where a largecrystal grain is obtained. Further, the area other than that of thelarge crystal grain is the microcrystal area where countless nucleationhas taken place, or the amorphous area; the size of the crystals is noteven and the roughness of the crystal surface is extremely large.

Accordingly, the irradiation condition, which is generally used inmanufacturing of semiconductor devices, is the condition where evencrystal grain size of approximately 0.1 μm-0.5 μm can be obtained.

Further, according to “Sequential lateral solidification of thin siliconfilms on SiO₂, Robert S. Sposili and James S. Im, Appl. Phys. Lett.69(19), Nov. 4, 1996, pp2864-2866”, James S. Im et al. disclosed aSequential Lateral Solidification method (hereinafter, referred to asSLS method), in which, by controlling artificially, the super lateralgrowth can be obtained at a desired position. According to the SLSmethod, an excimer laser beam of pulse oscillation is irradiated to amaterial via a slit-like mask. According to the SLS method, thecrystallization is carried out while the relative position between thematerial and the laser beam is displaced, at every shot, by a distance(approximately 0.75 μm), which is roughly equivalent to the length ofthe crystal formed via the super lateral growth; thereby, the crystal isallowed to grow by means of artificially controlled super lateralgrowth.

As described above, by using the SLS method it is possible to preparecrystal grains at desired positions under artificially controlledconditions, in a manner of the super lateral growth. However, the SLSmethod has the following problems as described below.

First of all, the problem is that the substrate processing efficiency(throughput) is insufficient. As described previously, in the SLSmethod, the crystallization distance per shot of laser beam isapproximately 1 μm. Accordingly, it is necessary that the relative shiftdistance (feed pitch) of the laser beam between the beam spot on thematerial surface and the material substrate is 1 μm or less. In theconditions adopted in the ordinary laser crystallization using a pulseoscillation excimer laser, feed pitch per shot of laser beam is several10 μm or more. Needless to say, under such conditions, the crystalpeculiar to the SLS method can not be prepared. In the SLS method,although a pulse oscillation XeCl excimer laser is used, the maximumoscillation frequency of the pulse oscillation XeCl excimer laser is 300Hz. Under such conditions, only the crystallization area of maximum 300μm or so is processed in distance in the scan direction of the laserbeam. At the processing speed as described above, in the case of a largesize substrate such as, for example, 600 mm×720 mm in dimension, withthe SLS method, it takes an extremely long period of time to process onesheet of substrate.

The fact that it takes a long processing time per sheet of substrate isnot only the problem of time and cost. That is to say, practically, inthe case of crystallization of an amorphous semiconductor film, thesurface processing thereof is critical. For example, in the case thatlaser irradiation is carried out after removing natural oxide film withdilute hydrofluoric acid or the like as a pre-processing, in the surfaceof the substrate, compared to the area where is subjected to the laserirradiation at the first, there is a possibility that natural oxide filmgrows again in the area where is subjected to the laser irradiation atthe last. In this case, amount of Carbon, Oxygen, Nitrogen, or amount ofcontamination impurities such as Boron or the like, which is taken inthe finished crystal, may vary within the surface of the substrateresulting in an unevenness of the transistor characteristics within thesurface of the substrate.

Secondly, such a problem that the optical system tends to be complicatedremains in the conventional SLS method. It is necessary to incorporate amask, which processes slit-like the configuration of the laser beampower at the substrate surface, into the optical system. Ordinarily,film thickness of an active layer silicon, which is used forpolycrystalline silicon thin film transistor, is several tens nm ormore. When a pulse oscillation excimer laser is used, the laser energydensity necessary for the laser crystallization is at least 200 mJ/cm²(as a typical example, for an amorphous silicon film of 50 nm,approximately 40 mJ/cm² with an XeCl excimer laser of 30 n sec pulsewidth). In the SLS method, there is a super lateral growth condition,which is the optimum for a further slightly stronger energy densityarea. It is difficult to prepare a slit-like form mask, which is capableof enduring such strong laser energy density. In the case of the mask ofmetal material, being subjected to the pulse laser beam irradiation of astrong energy density, the temperature of local film is raised andcooled down rapidly. As a result, it may cause a peeling or decay ofconfiguration of a minute pattern due to a long period of use (as forphoto lithography for resist exposure, although a hard mask materialsuch as chromium or the like is used, since incomparably weaker energydensity than the laser energy density necessary for siliconcrystallization is used, there is no problem such as peeling or a decayof configuration of the minute pattern). As described above, there issuch a factor that optical system becomes complicated resulting in adifficulty of maintenance of an apparatus in the conventional SLSmethod. Further, in order to carry out the super lateral growth, it isnecessary to make the spatial beam power profile of the laser beam sharp(to eliminate attenuation area of the optical power between theirradiation area and the non-irradiation area of the laser beam). In theconventional SLS method, since the beam necessary for the super lateralgrowth cannot be condensed using the ordinarily optical system only, theexcimer laser is used. Accordingly, it is understood that a slit-likemask is required to shield the laser beam partially.

The object of the invention is to solve the above-described problem, andfurther, to increase the positional control of crystal grains inaccordance with the layout of the TFT, and simultaneously, to increasethe processing speed of the crystallization process. More particularly,it is an object of the invention to provide a manufacturing method ofsemiconductor devices, which is capable of forming large size crystalgrains successively in a manner of super lateral growth under anartificial control, and capable of increasing the substrate processingefficiency in the laser crystallization process.

Further, the invention provides a manufacturing method of semiconductordevices which is capable of forming large size crystal grainssuccessively in a manner of super lateral growth under an artificialcontrol, and capable of increasing the substrate processing efficiencyin the laser crystallization process, as well as to provide amanufacturing method using a convenient laser irradiation method whichdoes not need to incorporate a mask, which processes the configurationof the laser beam power into a slit-like shape on the substrate surface,into an optical system unlike the conventional SLS method.

SUMMARY OF THE INVENTION

A laser irradiator applied to the invention includes a first means forcontrolling the irradiation position of laser beam with respect to anobject to be processed (substrate and thin film formed on thesubstrate); a second means (laser oscillator) for oscillating the laserbeam; a third means (optical system) for processing the laser beam; anda fourth means for controlling the oscillation of the second means, andfor controlling the first means so that the beam spot of the laser beam,which is processed by the third means, covers the specified position inaccordance with data (pattern information) of photomask configuration.

As the first means for controlling irradiation position of the laserbeam with respect to the object to be processed, two methods areavailable. One of the methods is a method in which the position of theobject to be processed placed on the stage is changed by driving thestage by means of a stage controller. The other one is a method in whichthe irradiation position of the laser beam spot is shifted using a laseroptical system in a state that the substrate position is fixed. In theinvention, any one of the above-described two methods is applicable; anda method, in which the above-described two methods are combined, is alsoapplicable.

The position specified in accordance with the data (pattern information)of photomask configuration is the portion in a semiconductor film, whichbecomes a channel area, a source area or a drain area in the thin filmtransistor, and is obtained by carrying out patterning processing bymeans of photo lithography technique on an island-like semiconductorlayer B after crystallization.

Also, in the invention, before the laser beam irradiation, it isnecessary to subject the semiconductor to an patterning processing on anisland-like semiconductor film A, which is specific area including anactive layer forming area comprised of thin film transistor by means ofphoto lithography technique, and to form markers on parts ofsemiconductor film. The marker is necessary to realize theabove-described fourth means. Further, the island-like semiconductorlayer A is slightly larger than the island-like semiconductor layer B.FIG. 2 shows a portion 500 as an example of the island-likesemiconductor layer A, and a portion 501 as an example of theisland-like semiconductor layer B. That is to say, it is a mode that theisland-like semiconductor layer B, which will finally become a channelarea, a source area and a drain area of the transistor is included inthe island-like semiconductor layer A.

Using the laser irradiator, which has the above-described first means tofourth means, the island-like semiconductor layer A is crystallized. Atthis time, using the fourth means, a part which is left as island-likesemiconductor layer B on the substrate after patterning processing inthe semiconductor film, which has been formed on the insulation surface,is comprehended in accordance with the data of the photomaskconfiguration. And, the laser beam is irradiated selectively to theisland-like semiconductor layer A to crystallize the area using themarker as the positional reference.

Next, the periphery portion of the island-like semiconductor layer A issubjected to a etching by means of photo lithography technique, and theisland-like semiconductor layer B is subjected to a patterningprocessing. The island-like semiconductor layer B is used as the activelayer of the transistor.

As described above, according to the invention, the laser beam isirradiated in such a manner that, not the entire semiconductor in thesubstrate surface is scanned by the laser beam, but at least the minimumindispensable portion thereof is crystallized. That is to say, bycarrying out the patterning processing on the island-like semiconductorlayer B after the semiconductor has been crystallized, it is possible toreduce the time necessary for irradiating the laser beam to the portionto be removed. Owing to this, it is possible to reduce the timenecessary for laser crystallization and to increase the processing speedof the substrate.

It is necessary that, after forming the island-like semiconductor layerA, the laser beam irradiation is carried out; and after that, theisland-like semiconductor layer B, which will become the active layer ofthe transistor, is formed, to ensure the positional control of thecrystal grain in accordance with the layout of the TFT.

By applying the above-described constitution to the conventional SLSmethod, the problem in the conventional SLS method that substrateprocessing efficiency (throughput) is insufficient, is solved. Also, ameans for ensuring the positional control of the crystal grain inaccordance with the layout of the TFT is obtained.

Further, according to the invention, the time necessary for lasercrystallization can be reduced. And further, a method that increases theprocessing speed of the substrate and a method that ensures thepositional control of the crystal grain in accordance the layout of theTFT are obtained. Furthermore, unlike the conventional SLS method, thesimple method that does not need to incorporate a mask for processingthe configuration of laser beam power at the surface of the substrateinto the optical system is obtained.

In order to obtain the super lateral growth, it is necessary to changethe spatial energy distribution of the laser beam sharply in thedirection of the lateral crystal growth (i.e., the direction in whichthe solid-liquid interface of the semiconductor film after laserirradiation). That is to say, it is necessary to eliminate theattenuation area width of optical power, which resides between theirradiation area and the non-irradiation area of the laser beam, as muchas possible. The attenuation area width capable of obtainingsatisfactory super lateral growth is defined as below; i.e., theattenuation area width from the peak position of the optical power to apoint where the power decreases to 50% is 10 μm or less.

In the conventional SLS method, since an excimer laser is used, thedensity necessary for the super lateral growth cannot be obtained by theordinary optical system only. Accordingly, it is understandable that aslit-like mask is necessary to be used to shield the laser beampartially.

The light source of the above-described laser beam is a system thatirradiates the second harmonic (or, third harmonic or fourth harmonic)of the solid-state laser oscillator of pulse oscillation. Compared tothe excimer laser, in the solid state laser, as the spreading angle ofthe output laser beam is small, owing to the laser constitution, with acylindrical lens only that is used as ordinary optical system lens, itis possible to condense the beam into a spatial beam power profile ofthe laser beam that is the optimum for the super lateral growth.

In order to increase the substrate processing efficiency, it is desiredto select a repeat frequency and a feed pitch that is the optimum forthe SLS method. The conditions for that will be described below. Theword “feed pitch” means shift distance of the substrate stage per pulseof the laser beam. In the SLS method, since the distance of the superlateral growth per shot is limited to a specific length, by enlargingthe feed pitch only, the substrate processing efficiency cannot beincreased. When the feed pitch is increased, it is necessary to increasealso the repeat frequency of the laser beam accordingly. The XeClexcimer laser used in the conventional SLS method is maximum 300 Hz. Onthe other hand, the solid-state laser oscillator of pulse oscillationcan increase the repeat frequency to the maximum several MHz.Accordingly, compared to the conventional SLS method, the processingcapacity can be largely increased by driving the solid-state laseroscillator of pulse oscillation to irradiate at a repeat frequency. Theupper limit of the repeat frequency can be determined within a rangethat ensures the energy density necessary for the super lateral growthat every shot of laser beam. The upper limit depends on the maximumoutput of the solid-state laser oscillator of pulse oscillation. (Since,if the other conditions are the same, when the frequency is increased,the energy density at every laser pulse is reduced.)

Further, in the solid-state laser oscillator, not the conventional flashlamp excitation but semiconductor laser excitation solid-state laseroscillator increases the stability of the laser beam energy largely. Asa result, it is possible to form a semiconductor of which crystallinityfluctuation is smaller. Accordingly, it is possible to manufacturesemiconductor device of which fluctuation in TFT characteristics issmaller.

Further, compared to the excimer laser irradiator, the solid-state laseroscillator is superior in maintainability.

Furthermore, compared to the excimer laser irradiator, the pulse widthof the solid-state laser is longer. Since the time for melting andcrystallizing becomes longer by adopting the longer pulse width, largercrystal grain can be formed.

Still further, by elongating the pulse width, it is possible to reducethe temperature difference between the semiconductor surface, where isto be irradiated by the laser, and the interface (for example, basefilm) between the semiconductor film and the film abutting to the bottomface thereof. As described above, by reducing the temperaturedifference, the core generating speed becomes slower.

FIG. 14 shows a result of simulation of the relationship between thepulse width and the base film temperature at crystallization. When themaximum reached temperature of the semiconductor surface is 1500K, 2000Kand 2500K respectively, the temperature of the base film tends to becomehigher as the pulse width is longer, and then, the level of thetemperature becomes fixed. Also, when the pulse width is larger than 50ns, and preferably, larger than 100 ns, it is possible to reduce thetemperature difference between the base film temperature and the maximumreached temperature of the interface, it is possible to make the coregenerating speed more slowly.

The following table show a comparison between the XeCl gas laserirradiator and the Nd:YLF solid-state laser irradiator in the SLSmethod.

TABLE 1 XeCl excimer laser irradiator Nd: YLF solid state laser Lasermedium Gas (XeCl) Solid state (Nd: YLF) Excitation method High voltageDPSS (Diode excitation) Maintenance Necessary Maintenance free Pulsewidth Approx. 25 nsec 50-200 nsec Beam length Less than 300 mm 30-50 mm(Plural units available) Machine price 100 million or less 18 millionMask Necessary Mask-less Optical system Complicated Simple (convex and(homogenizer, cylindrical lens) projection lens, etc)

Owing to the constitution as described above, it is possible to providea manufacturing method of semiconductor devices which is capable offorming large size crystal grains successively in a manner of superlateral growth under an artificial control, and capable of increasingthe substrate processing efficiency in the laser crystallizationprocess, as well as to provide a manufacturing method using a convenientlaser irradiation method which does not need to incorporate a mask,which processes the configuration of the laser beam power into aslit-like shape on the substrate surface, into an optical system unlikethe conventional SLS method.

The word “semiconductor device” in the invention includes everyapparatus that is capable of functioning by using the semiconductorcharacteristics (for example, electronic device represented by liquidcrystal display and electronic apparatus equipped with the electronicdevice as a part thereof).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a laser irradiatorused in the invention;

FIG. 2 is an illustration showing a laser beam spot, which shifts atevery pulse with respect to an object to be processed;

FIGS. 3A and 3B are illustrations showing a laser beam irradiation spotof which relative movement direction within a substrate is changed bymeans of rotation of the substrate;

FIGS. 4A and 4B are illustrations showing a relationship between thechannel length direction of a transistor and a laser beam spot in arelative movement;

FIGS. 5A and 5B are illustrations showing marker-forming portions;

FIGS. 6A to 6D are illustrations showing a manufacturing method of anactive matrix substrate;

FIGS. 7A to 7C are illustrations showing a manufacturing method of anactive matrix substrate;

FIGS. 8A to 8C are illustrations showing a manufacturing method of anactive matrix substrate;

FIG. 9 is an illustration showing a manufacturing method of an activematrix substrate;

FIGS. 10A and 10B are illustrations of an optical system of the laserirradiator, which will be described in Embodiment 1;

FIG. 11A is a picture showing a surface SEM image after lasercrystallization;

FIG. 11B is an illustration showing a status of crystal grain boundary;

FIGS. 12A to 12L are illustrations showing a manufacturing method of asemiconductor device using a laser irradiation method according to theinvention, which will be described in Embodiment 2;

FIGS. 13A to 13C are illustrations showing a manufacturing method of asemiconductor device using a laser irradiation method according to theinvention, which will be described in Embodiment 4;

FIG. 14 is a graph showing a simulation of a relationship between pulsewidth and base film temperature at crystallization.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, referring to the figures attached hereto, the mode for carrying outthe invention will be described in detail.

FIG. 1 shows a block diagram illustrating a laser irradiation methodaccording to the invention. In FIG. 1, two methods are shown as a firstmeans, respectively, for controlling irradiation position of the pulselaser beam with respect to an object to be processed 107. One of themethods is such a method that the position of the object to be processed107 (substrate), which is placed on a stage 108, is changed by drivingthe stage 108 by means of a stage controller 101. The other method issuch a method that, in a state that the substrate position is fixed, theirradiation position of the laser beam spot is shifted using an opticalsystem 103. In the invention, either one of methods may be adopted; or,a method, in which the above-mentioned two methods are combined witheach other, may be adopted.

In the above-described two methods, both of them means the fact thatrelative position of the laser beam spot position with respect to thesubstrate is changed. Hereinafter, it will be referred to as “to scan(the laser beam spot)”.

Also, a laser irradiator 100 has a pulse laser oscillator 102 which is asecond means that oscillates the pulse laser beam. The pulse laseroscillator 102 can be appropriately replaced with another one inaccordance with the processing object. Further, two pulse laseroscillators may be used being combined with each other. In theinvention, a well-known laser may be used. As for the laser, a gas laseroscillator or a solid-state laser oscillator of pulse oscillation may beused. When a pulse oscillation gas laser is used, only a control bymeans of a photomask-like data pattern, which uses a computer 104 isapplied thereto, and other constitution conforms to an ordinary SLSmethod. In the mode for carrying out the invention, a case, in which asolid-state laser oscillator of pulse oscillation is used, will bedescribed.

As for the solid-state laser oscillator of pulse oscillation, as a lightsource, one or a plurality of kinds of lasers selected from YAG laser,YVO₄ laser, YLF laser, YAl0₃ laser, glass laser, ruby laser, alexandritelaser, Ti: sapphire laser, forsterite laser (Mg₂SiO₄) oscillator, whichare doped with Cr³⁺, Cr⁴⁺, Nd³⁺, Er³⁺, Ce²⁺, Co²⁺, Ti³⁺, Yb³⁺, or V³⁺ asa impurity, may be given.

As for the fundamental wave of the relevant laser, a laser beam having afundamental wave of 1 μm or so is obtained, but it varies depending onthe doping material. A second harmonic, a third harmonic, and a fourthharmonic with respect to the fundamental wave can be obtained by using anon-linear optical element.

Further, the laser irradiator 100 has an optical system 103 equivalentto the third means, which is capable of processing a beam spot of thelaser beam oscillated by the pulse oscillator 102 in the object to beprocessed. The shape of the laser beam output from the pulse oscillator102 is formed into a circular shape if the shape of the rod is circular;if the rod is slab-like shape, the shape thereof is formed into arectangular shape. By further reforming the laser beam asdescribed-above with the optical system, it is possible to form the beamspot of laser beam at the surface of the object to be processed 107.Further, depending on the purpose of the processing, a telescope, ahomogenizer or the like may be incorporated into the optical system 103to process the beam.

Furthermore, the laser irradiator 100 has a computer 104, which isequivalent to the fourth means. The computer 104 controls theoscillation of pulse oscillator 102, and controls stage controller 101,which is equivalent to first means, so that the beam spot of the laserbeam covers a position specified by the data of a mask pattern.

In addition to the above described four means, this laser irradiationmethod may include a means for controlling the temperature of the objectto be processed.

FIG. 2 shows a state that the relative position between the substrateand the laser beam spot is displaced (to be scanned) at every laser beampulse. Enlarged views of beam spots 507 a, 507 b and 507 c are shown.

Reference symbol 507 a in FIG. 2 denotes a laser beam spot position at apulse irradiation; 507 b denotes the laser beam spot position at thenext pulse irradiation; and 507C denotes the laser beam spot position atthe further next pulse irradiation. Reference symbols 509 a and 509 bdenote substrate stage shift distance (feed pitch), respectively, atevery one pulse of the laser beam. The feed pitch is required to be 0.3μm or more and 5 μm or less, more preferably, to be 0.7 μm or more and 3μm or less.

Further, as for the beam, the energy density at the edge portion of thelaser beam is generally lower than the other portion, processing on theobject to be processed may not be made evenly. Accordingly, it ispreferred that the laser beam is irradiated so that the edge portion inthe longitudinal direction of the beam spot 507 a of the laser beam doesnot overlap with the potion 500 equivalent to an island-likesemiconductor film A, which is obtained by patterning the semiconductorfilm after crystallization. For example, when scanning the beam spot oflinear form, it is adapted so that the area, which is denoted byreference numeral 508 in FIG. 2, is not irradiated in the portion 500equivalent to the above-described island-like semiconductor film A.

When the semiconductor after crystallization is used as the active layerof the TFT, it is preferred to fix the scan direction so as to beparalleled to the direction in which the carrier in the channel formingarea moves. This is shown in FIG. 4A and FIG. 4B. Reference numerals 529and 539 in FIG. 4 denote the island-like semiconductor layer A,respectively, which is formed before laser irradiation. Referencenumerals 528 and 538 denote the area, respectively, which is formed asan island-like semiconductor layer B after laser irradiation.

FIG. 4A shows an example of an active layer of a single gate TFT whichis provided with one channel forming area. A channel forming area 520,which comprises the island-like semiconductor layer B, and impurityareas 521 and 522, which will become a source area or a drain area,respectively, are provided. When crystallizing the semiconductor usingthe laser oscillator according to the invention, as shown with arrows,the scan direction of the laser beam is fixed so as to be paralleled tothe direction in which the carrier in the channel forming area moves(channel length direction). Reference numeral 523 denotes the beam spotof the laser beam, which scans in the directions indicated with thearrows.

Also, in FIG. 4B, an example of an active layer of triple gate TFT towhich three channel forming areas are provided is shown. Impurity areas533 and 534 are provided so as to sandwich a channel forming area 530therebetween; further, impurity areas 534 and 535 are provided so as tosandwich a channel forming area 531 therebetween; and furthermore,impurity areas 535 and 536 are provided so as to sandwich a channelforming area 532 therebetween. When the semiconductor is crystallizedusing the laser oscillator according to the invention, the laser beamscans in the direction of the arrows.

However, as a matter of convenience of circuit layout, as for the TFTused in active matrix display, the direction of carriers, moving intothe respective active layer channel forming areas, may sometimes bedifferent from each other, in the pixel section, the signal line drivecircuit section, and the scan line drive circuit section. In such a casealso, the invention is effective, and that will be described referringto FIG. 3.

FIG. 3 shows a case that the scan directions of the laser beam in thescan line drive circuit area 512 is different from those in the otherareas. First of all, using the markers formed on the substrate as thepositional references, as shown in FIG. 3A, area 511, which will becomea signal line drive circuit, and area 510, which will become a pixelsection, are subjected to the laser irradiation.

Next, as shown in FIG. 3B, the substrate stage is turned by 90° and themarkers formed on the substrate are read again. Based on the positionalinformation, the area 512, which will become a scan line drive circuitis subjected to the laser irradiation. Thus, it is possible to changethe relative shift direction of the laser beam spot within the substrateand to irradiate the same.

Further, there may be a case that, even when the laser irradiation isbeing carried out, the laser beam should not be irradiated temporarilyto the surface of the substrate. In this case, an AO (acoustooptics)light modulation device, which is capable of temporarily and completelyshielding the laser beam, maybe provided in an optical system betweenthe substrate, which is the object to be processed and the laseroscillator.

In order to determine the irradiation position of the laser beam, it isnecessary to form the markers for positioning with respect to thesemiconductor film thereon. FIG. 5 shows the positions where markers areformed in a semiconductor film, which is formed to prepare an activematrix type semiconductor device. FIG. 5A shows an example of the casethat one semiconductor device is prepared from one substrate; FIG. 5Bshows the case that four semiconductor devices are prepared from onesubstrate.

In FIG. 5A, reference numeral 540 denotes an area where a semiconductorfilm is formed on the substrate; dotted line 541 denotes an area where apixel section is formed; dotted line 542 denotes an area where a signalline drive circuit is formed; dotted line 543 denotes an area where ascan line drive circuit is formed. Reference numeral 544 denotes areaswhere a marker is formed (marker forming portion), and are provided tobe positioned at four corners of the semiconductor.

In FIG. 5A, although the marker forming portion 544 is provided at fourcorners respectively, the invention is not limited thereto. Assumingthat the positioning of the scan area of the laser beam in thesemiconductor and the patterning mask of the semiconductor is obtained,the position and number of the marker forming portions are not limitedto the mode described-above.

In FIG. 5B, reference numeral 550 denotes a semiconductor formed on thesubstrate; dotted line 551 denotes a scribe line, which is used to cutoff the substrates in the later process. In FIG. 5B, by cutting off thesubstrates along the scribe line 551, four semiconductor devices can bemanufactured. The number of the semiconductor devices, which areobtained by cutting off, is not particularly limited to this.

Reference numeral 552 denotes a portion a marker is formed (markerforming portion), and is provided at four corners of the semiconductor.In FIG. 5B, although the marker forming portion 552 is provided at fourcorners respectively, the invention is not limited thereto. Assumingthat the positioning of the scan area of the laser beam in thesemiconductor and the patterning mask of the semiconductor film isobtained, the position and number of the marker forming portions are notlimited to the mode described-above.

The markers are formed simultaneously in the conventional photolithography process in which the island-like semiconductor film A isformed in a manner of patterning.

Owing to the constitution as described above, after crystallizing thesemiconductor, it is possible to reduce the time necessary for the laserbeam irradiation and the processing speed of the substrate can beimproved, because it can omit the time necessary for irradiating thelaser beam to the semiconductor area, which is removed due to theforming of island-like semiconductor film B.

EXAMPLES Example 1

Referring to FIGS. 6 to 9, in the Example 1, a manufacturing method ofactive matrix substrate will be described. Herein, as a matter ofconvenience, a substrate, which is formed with a CMOS circuit, a drivecircuit, and a pixel section having a pixel TFT and a holding capacityon the same substrate, will be called as active matrix substrate.

First of all, in the Example 1, a substrate 600 comprised of a bariumborosilicate glass or an aluminum borosilicate glass or the like isused. As for the substrate 600, a substrate formed with an insulatingfilm on the surface of a quarts substrate, a silicon substrate, a metalsubstrate or a stainless substrate may be used. Also, a plasticsubstrate having heat resistance against the processing temperature ofthe Example 1 may be used.

Then, on the substrate 600, a base film 601 comprised of an insulatingfilm of a silicon dioxide film, a silicon nitride film, or a siliconoxide nitride film or the like is formed in a manner of well-known means(sputtering, LPCVD, plasma CVD or the like). According to the Example 1,as a base film 601, a double-layered base film comprised of base films601 a and 601 b is used. However, a structure of a single-layered ordouble-layered film of the above-described insulating film may be used(FIG. 6A).

Next, on the base film 601, an amorphous semiconductor film 692 isformed at a thickness of 25-150 nm (preferably, 30-120 nm) in a mannerof a well-known means (sputtering, LPCVD, plasma CVD or the like) (FIG.6A). According to the Example 1, although an amorphous semiconductorfilm is formed, a micro crystal semiconductor film or a crystalsemiconductor film is also applicable. Further, a chemical compoundsemiconductor having an amorphous structure of an amorphous silicongermanium film or the like may be used.

Next, the amorphous semiconductor film 692 is subjected to a patterning,and by carrying out an etching in a manner of anisotropic dry etching inan atmosphere containing a halogen fluoride, for example, CIF, CIF₃,BrF, BrF₃, IF, IF₃ or the like, portions 693 a, 693 b and 693 c, whichwill become an island-like semiconductor film A respectively, are formed(FIG. 6B).

Next, the portions 693 a, 693 b and 693 c on the island-likesemiconductor film A are crystallized in a manner of lasercrystallization. The laser crystallization is carried out using thelaser irradiation method according to the invention. Particularly, inaccordance with mask information input in the computer of the laserirradiator, a laser beam is irradiated selectively to the portions 693a, 693 b and 693 c on the island-like semiconductor film A. Needless tosay, not only the laser crystallization, but also, the crystallizationmay be carried out in a combination with another well-knowncrystallization method (RTA, heat crystallization using furnaceannealing, heat crystallization using a metal element, which acceleratethe crystallization, or the like).

In the laser irradiation method according to the invention, a gas laseroscillator or a solid-state laser oscillator of pulse oscillation inwell-known laser sources is usable. When a gas laser of pulseoscillation is used, only a control by means of data pattern ofphotomask configuration using a computer 104 is applied thereto, and theother constitution conforms to ordinary SLS method. In Example 1, thecase, in which an Nd:YLF laser of pulse oscillation is used, will bedescribed.

FIGS. 10A and 10B show a laser crystallization processing apparatus.FIGS. 10A and 10B show a case, in which an Nd:YLF laser oscillator lasersource 1101 is used under the conditions of 1.5 W output and 1 kHzrepeat frequency. The laser source 1101 is a method, in which an YLFcrystal and a non-linear optical element is placed in a resonator, and asecond harmonic of 527 nm wavelength is output. Needless to say, thenon-linear optical element may be placed outside the resonator. Further,as for the laser oscillator 1101, the rod is cylindrical inconfiguration, and the configuration of the beam spot immediately afteroutput from the laser oscillator 1101 is circular. Even when theconfiguration of the rod is slab-like shape and the configuration of thebeam spot immediately after output is rectangular shape, as describedbelow, the beam spot can be reformed into a desired configuration bymeans of optical system.

As for the Nd:YLF laser, the spreading angle of the beam is 3 mm radian;although the beam size is approximately 2 mm in diameter at the outletport, it expands to approximately 1 cm in diameter at a position 20 cmaway from the outlet port. When a convex lens 1102 of focal length f=600mm is placed at this position, the beam is reformed into a parallel beamof 10 mm in diameter. The laser beam, which is reflected by the opticalmirrors 1103-1105 shown in FIG. 10A, is condensed by a convexcylindrical lens 1106 having the curvature in the direction of Y in FIG.10A. Herein, the Y-direction is the shift direction of the beam spot ofthe laser beam on the semiconductor surface, and is the shorterdirection of the beam spot. Also, the X-direction in FIG. 10A is thelongitudinal direction of the beam spot of the laser beam on thesemiconductor surface, and crosses at right angles with the shiftdirection of the beam spot of the laser beam on the semiconductorsurface (optical mirrors 1103-1105 are placed on the ground of thelayout of the apparatus, but it is not always indispensable). Owing tothe constitution as described above, the beam spot on the semiconductorsurface, which is the irradiation surface, is reformed into a linearshaped beam of 10 mm×10 μm.

However, the method of reforming the laser beam of rectangular,elliptical or linear shape at the irradiation surface is not limited tothe above. Although not shown in the figures, it is possible to elongatethe beam spot in longitudinal direction by placing a concave cylindricallens between the optical mirror 1103 and the convex cylindrical lens1106. Also it is possible to place a beam collimator for reforming thelaser beam into a parallel beam or a beam expander for expanding thelaser beam between the concave cylindrical lens and the laser oscillator1101. A method of reforming a beam into a linear shaped beam using alaser source of 1.5 W output with a beam spot of 10 mm×10 μm has beendescribed here. However, in the case of a larger output laser source, itis preferred that the beam spot size in the longitudinal direction onlyis enlarged without changing the beam spot size in the shorter direction(currently, an oscillator of LD excitation Nd:YLF laser, which isoperable at 20V output, is commercially available).

In order to shift the relative position of the beam spot of the laserbeam on the semiconductor surface, a substrate stage 1109 is made tosweep in the Y-direction (shorter direction of the beam spot). When thesweep speed of the substrate stage is 3.0 mm/sec. at 1 kHz laser pulserepeat frequency, at every irradiation of the laser pulse, the relativeposition between the substrate and the beam spot displaces by 3 μm inthe Y-direction (feed pitch is 3 μm).

FIG. 11A is a SEM observation of a silicon film, which has beencrystallized by means of the laser irradiation method according to theExample 1, in which crystal grain boundary is visualized in a manner ofSecco Etching. FIG. 11B and FIG. 11A show the crystal grain boundary andthe size thereof so as to be understood easily. Referring to this, it isunderstood that crystals, which have been subjected to the super lateralgrowth in the Y-direction of the scanned beam spot of the laser beam,are formed continuously. The grain boundaries reside periodically in thescan direction and the vertical direction of the laser beam spot. It isunderstood that the period correspond to 3 μm, which is the feed pitchof the laser pulse at every irradiation.

Owing to the above described laser crystallization, portions 694 a, 694b and 694 c of island-like semiconductor film A, of which crystallinityhas been increased (FIG. 6C).

Next, by patterning the portions 694 a, 694 b and 694 c of theisland-like semiconductor film A into a desired configurationrespectively, portions 602-606 of an island-like semiconductor film Bare formed (FIG. 6D).

After forming the portions 602-606 of the island-like semiconductor filmB, in order to control the threshold of the TFT, minute amount ofimpurity element (Boron or phosphorous) may be doped. The impuritydoping for controlling the threshold may be carried out before the lasercrystallization, or after forming a gate insulating film.

Next, a gate insulating film 607 that covers island-like semiconductorfilms 602-606 is formed. The gate insulating film 607 is formed with aninsulating film, which contains silicon, of 40-150 nm in thickness in amanner of plasma CVD or sputtering. According to the Example 1, the gateinsulating film 607 is formed with a silicon nitride oxide film(constitution ratio: Si=32%, O=59%, N=7% and H=2%) at 110 nm inthickness in the manner of plasma CVD. Needless to say, the gateinsulating film is not limited to the silicon nitride oxide film, butanother insulating film, which contains silicon, may be formed into asingle-layered or laminated structure.

Further, when a silicon dioxide film is used, the gate insulating filmcan be formed in a manner of the plasma CVD, by mixing TEOS (TetraethylOrtho Silicate) and O₂; at 40 Pa reaction pressure and 300-400° C.substrate temperature, and by discharging high frequency (13.56 MHz) at0.5-0.8 W/cm² of electric power density. The silicon dioxide filmprepared in the above-described manner is subjected to a heat anneal at400-500° C., thereby excellent characteristics as the gate insulatingfilm are obtained.

Next, formed on the gate insulating film 607 is a first conductive film608 of 20-100 nm in film thickness and a second conductive film 609 of100-400 nm in film thickness. According to the Example 1, the firstconductive film 608 comprised of a TaN film of 30 nm in film thicknessand the second conductive film 609 comprised of a W film of 370 nm infilm thickness are built-up to form a laminated layer. The TaN film isformed in a manner of sputtering using a target of Ta, and sputtering inan atmosphere containing Nitrogen. Also, the W film is formed in amanner of sputtering using a target of W. Other than the above, theabove-described film may be formed in a manner of thermal CVD usingTungsten hexafluoride (WF₆). In any case, to use the film as the gateelectrode, it is necessary to lower the resistance, and as for theresistance of the W film, it is desired to be less than 20 μΩcm. As forthe W film, although it is possible to lower the resistance by forminglarger crystal grains, in the case that a large amount of impurityelement such as oxygen or the like is contained in the W film, thecrystallization is inhibited resulting in a larger resistance.Therefore, according to the Example 1, by carrying out the sputteringusing a high purity W (purity level: 99.9999%) as a target, andfurthermore, while paying a great attention not to allow any impurity tocome in from the atmosphere during the film forming, the W film isformed achieving a resistance of 9-20 μΩcm.

According to the Example 1, the first conductive film 608 is formed withTaN and the second conductive film 609 is formed with W. However, theabove is not limited thereto. In any case, the film may be formed withan element selected from Ta, W, Ti, Mo, Al, Cu, Cr and Nd; or, the filmmay be formed with an alloy material containing the above element as themain component, or a compound material. Also, a semiconductorrepresented by a polycrystalline silicon film doped with impurityelement like phosphorous, or AgPdCu alloy may be used. Further, acombination of a first conductive film formed with a Tantalum (Ta) filmand the second conductive film formed with a W film; a combination of afirst conductive film formed with a Titanium nitride (TiN) film and thesecond conductive film formed with a W film; a combination of a firstconductive film formed with Tantalum nitride (TaN) and the secondconductive film formed with a W film; a combination of a firstconductive film formed with Tantalum nitride (TaN) and the secondconductive film formed with an Al film; or a combination of a firstconductive film formed with Tantalum nitride (TaN) and the secondconductive film formed with an Cu film may be used.

Further, not limited to the double-layered structure, but, for example,a triple-layered structure, which is built-up with a Tungsten film, analloy film of aluminum and silicon (Al—Si) film and a Titanium nitridefilm in order may be used. Furthermore, when a triple-layered structureis adopted, a nitride Tungsten may be used in place of Tungsten; analloy film (Al—Ti) of aluminum and Titanium in place of the alloy(Al—Si) film of aluminum silicon may be adopted; and a Titanium film maybe used in place of the Titanium nitride film.

It is important to collect the optimum etching method and type of theetchant depending on the material of the conductive film.

Next, using a photo lithography, masks 610-615 comprised of a resist areformed, and are subjected to a first etching processing to formelectrodes and wirings. The first etching processing is carried outunder the first and the second etching condition S (FIG. 7B). Accordingto the Example 1, as for the first etching conditions, ICP (InductivelyCoupled Plasma) etching is adopted; as for etching gases, CF₄, Cl₂ andO₂ are used and the gas flow rate is 25:25:10 (sccm) respectively. Undera pressure of 1 Pa, an RF (13.56 MHz) electric power of 500 W is appliedto coil type electrode to generate plasma, and the etching is carriedout. To the substrate side (object stage) also, an RF (13.56 MHz)electric power of 150 W is supplied to impress a substantially negativeself-bias voltage thereto. Under the first etching conditions, theW-film is subjected to the etching to form the edge of the firstelectrical conducting layer into a tapered configuration.

After that, without removing the masks 610-615 comprised of a resist,the etching condition is changed to second etching conditions. As forthe etching gases, CF₄ and Cl₂ are used, and the gas flow rate is 30:30(sccm) respectively. Under a pressure of 1 Pa, an RF (13.56 MHz)electric power of 500 W is supplied to the coil type electrode togenerate plasma, and the etching is carried out approximately for 30seconds. To the substrate side (object stage) also, an RF (13.56 MHz)electric power of 20 W is supplied to impress a substantially negativeself-bias voltage thereto. Under the second etching conditions, in whichCF₄ and Cl₂ are mixed, both of the W film and the TaN film are etched tothe same level. To carry out the etching without remaining any residueon the gate insulating film, it is preferred to increase the etchingtime by approximately 10-20%.

In the above-described first etching processing, By adaptingappropriately the configuration of the mask comprised of a resist, theedge of the first electrical conducting layer and the second electricalconducting layer are formed into a tapered configuration, owing to thebias voltage, which is applied to the substrate side. The angle of thetapered portion is 15-45°. Owing to the first etching processing, theelectrical conducting layers 617-622 (first electrical conducting layers617 a-622 a and second electrical conducting layers 617 b-622 b) of afirst configuration, which are comprised of the first electricalconducting layer and the second electrical conducting layer, are formed.Reference numeral 616 denotes a gate insulating film, and the areasthereof, which are not covered by the electrical conducting layers617-622 of the first configuration are formed into thin areas which hasbeen etched approximately 20-50 nm.

Next, without removing the mask comprised of a resist, a second etchingprocessing is carried out (FIG. 7C). In this case, as for the etchinggases, CF₄, Cl₂ and O₂ are used, and the W-film is selectively etched.And then, by means of the second etching processing, second electricalconducting layers 628 b-633 b are formed. On the other hand, the firstelectrical conducting layers 617 a-622 a are little etched, andelectrical conducting layers 628-633 of a second configuration areformed.

Then, without removing the mask comprised of a resist, a first dopingtreatment is carried out, an impurity element that imparts the N-type tothe island-like semiconductors at a low density. The doping treatmentmay be carried out in a manner of ion doping or ion implantation. As forthe conditions for the ion doping, dose amount is 1×10¹³-5×10¹⁴atoms/cm²; and the acceleration voltage is 40-80 keV. According to theExample 1, the dose amount is 1.5×10¹³ atoms/cm²; and the accelerationvoltage is 60 keV.

As an impurity element imparting the N-type, although an elementincluded in the 15-family, typically, phosphorous (P) or Arsenic (As) isused, phosphorous (P) is used in the Example 1. In this case, electricalconducting layers 628-633 serve as the masks against the impurityelement imparting the N-type, impurity areas 623-627 are formed in amanner of self-aligning. To the impurity areas 623-627, the impurityelement imparting the N-type within the density range of 1×10¹⁸-1×10 ²⁰atoms/cm³ is added.

After removing the masks comprised of a resist, new masks 634 a-634 ccomprised of a resist are formed, and are subjected to a second dopingtreatment at an acceleration voltage higher than that of the firstdoping treatment. As for the conditions for the ion doping, dose amountis 1×10¹³-1×10¹⁵ atoms/cm²; acceleration voltage is 60-120 keV. As forthe doping treatment, the second electrical conducting layers 628 b, 630b and 632 b are used as masks against the impurity element, and thedoping is carried out so that the impurity element is added to theisland-like semiconductors below the tapered portion of the firstelectrical conducting layer. Then, the acceleration voltage is reducedlower than that of the second doping treatment, and a third dopingtreatment is carried out to obtain a state shown in FIG. 8A. As for theconditions for the ion doping, dose amount is 1×10¹⁵-1×10¹⁷ atoms/cm²;and the acceleration voltage is 50-100 keV. Owing to the second dopingtreatment and the third doping treatment, to the low density areas 636,642 and 648 which overlap with the first electrical conducting layer, animpurity element imparting the N-type is added within the density rangeof 1×10¹⁸-5×10¹⁹ atoms/cm³; and to high density impurity areas 635, 641,644 and 647, an impurity element imparting the N-type is added withinthe density range of 1×10¹⁹-5×10²¹ atoms/cm³.

Of course, as for the second doping treatment and the third dopingtreatment, by adapting an appropriate acceleration voltage, it ispossible to form the low-density impurity area and the high-densityimpurity area, respectively, by one doping treatment.

Next, after removing the resist masks, new resist masks 650 a-650 c areformed, and are subjected to a fourth doping treatment. Owing to thefourth doping treatment, to the island-like semiconductors, which becomethe active layers of a P-channel type TFT, impurity areas 653, 654, 659and 660, added with an impurity element imparting a conductive typeopposite to the above-described conductive type, are formed. Using thesecond electrical conducting layers 628 b-632 b as the masks against theimpurity element, an impurity element imparting P-type is added to formimpurity areas in a manner of self-aligning. According to the Example 1,the impurity areas 653, 654, 659 and 660 are formed by means of iondoping using diborane (B₂ H₆) (FIG. 8B). When the fourth dopingtreatment is carried out, the island-like semiconductors for formingN-channel type TFT are covered with the masks 650 a-650 c comprised of aresist. Owing to the first to third doping treatment, to the impurityareas 653, 659 and 660, phosphorous is added at a density different fromeach other, respectively. By carrying out doping treatment so that, inany area of the above, the density of the impurity element impartingP-type is 1×10¹⁹-5×10²¹ atoms/cm³, since the impurity areas function asthe source area and the drain area of the p-channel type TFT, no problemoccurs.

By carrying out steps up to the step described above, impurity area isformed in the respective island-like semiconductors. Then, an activationprocessing is carried out. As for the activation processing, well-knownlaser activation, thermal activation or RTA activation is applicablethereto. Further, the laser activation-processing step may be done,after the first interlayer insulating film has been formed.

Then, the mask 650 a-650 c comprised of a resist is removed, and a firstinterlayer insulating film 661 is formed. As for the first interlayerinsulating film 661, using the method of plasma CVD or sputtering, theinsulating film, which contains silicon, is formed in thickness of100-200 nm. According to the Example 1, a silicon nitride-oxide film of150 nm in film thickness is formed by means of plasma CVD. Of course,the first interlayer insulating film 661 is not limited to the siliconnitride-oxide film. Another single or laminated layered insulating film,which contains silicon, may be used.

Then, by carrying out heat processing (heat treatment for 1-12 hours at300-550° C.), the film is hydrogenated. This process is for terminatingthe dangling bond of the island-like semiconductor by means of hydrogen,which is contained in the first interlayer insulating film 661.Irrespective of first interlayer insulating film, the island-likesemiconductor can be hydrogenated. As for another means for thehydrogenation, the film may be subjected to plasma hydrogenation(hydrogen excited by plasma is used), or to a heat treatment for 1-12hours at 300-650° C. in an atmosphere containing 3-100% of hydrogen.

Next, formed on the first interlayer insulating film 661 is a secondinterlayer insulating film 662 comprised of an inorganic insulation filmmaterial or an organic insulation material. According to the Example 1,an acrylic resin film of 1.6 μm in film thickness is formed using amaterial of 10-1000 cp, preferably, 40-200 cp in viscosity, which formsunevenness on the surface.

According to Example 1, in order to prevent specular reflexion,unevenness is formed on the surface of the pixel electrode by formingsecond interlayer insulating film, which is formed with unevenness onthe surface thereof. Further, in order to obtain light scattering bygiving unevenness to the pixel electrode, a convex portion may be formedin the area below the pixel electrode. In that case, since the convexportion can be formed using the same photomask as that for forming theTFT, the convex portion can be formed without increasing the number ofsteps. The convex portion may be formed appropriately on the substratein a pixel section area other than the wiring and TFT portions. Thus,unevenness is formed on the surface of the pixel electrode along theunevenness formed on the surface of the insulating film, which coversthe convex.

Further, a film of which surface is planarized may be used as the secondinterlayer insulating film 662. In that case, it is preferred that,after the pixel electrode is formed, a process such as well-knownsandblasting, etching or the like is added to make the surface thereofuneven to prevent specular reflexion, and thereby reflected light isscattered, resulting in a increased white level.

Next, after forming the second interlayer insulating film 662, a thirdinterlayer insulating film 672 is formed so as to come in contact withthe second interlayer insulating film 662.

Then, in a drive circuit 686, wirings 663-667 that connect therespective impurity areas with each other electrically, are formed.These wirings are formed by means of patterning a laminated filmcomprised of a Ti film of 50 nm in film thickness and an alloy film(alloy film of Al and Ti) of 500 nm in film thickness. Of course, notlimited to the double-layered structure, a single-layered structure or atriple-layered structure may be adopted. Also, the material for thewirings is not limited to Al and Ti. For example, the wirings may beformed by patterning a laminated film, in which Al or Cu is formed on aTaN film, and further thereon, a Ti film is formed (FIG. 9).

Further, in a pixel section 687, a pixel electrode 670, a gate wiring669 and a connecting electrode 668 are formed. Owing to the connectingelectrode 668, the source wiring (lamination of 633 a and 633 b) isformed with an electrical connection with the pixel TFT. Also, the gatewiring 669 is formed with an electrical connection with the gateelectrode of the pixel TFT. Further, the pixel electrode 670 is formedwith an electrical connection with a drain area 658 of the pixel TFT;and furthermore, formed with an electrical connection with theisland-like semiconductor 606 that functions as an electrodeconstituting a holding capacity. As for the pixel electrode 670, it ispreferred to use a material such as a film comprised of Al or Ag as themain component, a laminated film thereof, and so on, which is superiorin reflexivity.

By carrying out the steps described above, a CMOS circuit comprised ofan N-channel type TFT 681 and a P-channel type TFT 682, a drive circuit686 including an N-channel type TFT 683, and a pixel section 687including a pixel TFT 684 and a holding capacity 685 are formed on thesame substrate. Thus, an active matrix substrate is completed.

The N-channel type TFT 681 of the drive circuit 686 includes a channelforming area 637, the low density impurity area 636 (GOLD area), whichoverlaps with a first electrical conducting layer 628 a constituting apart of the gate electrode, and a high density impurity area 652 thatfunctions as the source area or the drain area. The P-channel type TFT682 that constitutes the CMOS circuit being connected with N-channeltype TFT 681 via an electrode 666 includes a channel forming area 640,the high density impurity area 653 that functions as the source area orthe drain area and the impurity area 654 introduced with an impurityelement imparting N-type and an impurity element imparting P-type.Further, the N-channel type TFT 683 includes a channel forming area 643,the low density impurity area 642 (GOLD area), which overlaps with afirst conductive layer 630 a constituting a part of the gate electrodeand a high density impurity area 656 that functions as the source areaor the drain area.

The pixel TFT 684 of the pixel section includes a channel forming area646, a low density impurity area 645 (LDD area) that is formed outsidethe gate electrode and a high density impurity area 658 that functionsas the source area and the drain area. The island-like semiconductorthat functions as an electrode of the holding capacity 685 is added withan impurity element imparting N-type and an impurity element impartingP-type. The holding capacity 685 is comprised of an electrode (laminatedlayers of 632 a and 632 b) using the insulating film 616 as thedielectric and an island-like semiconductor film.

In the pixel structure according to the Example 1, the end portion ofthe pixel electrode is disposed to overlap with the source wiring sothat the space between the pixel electrodes is shielded without usingany black matrix.

Example 2

In Example 2, a manufacturing method of a TFT using a laser irradiationmethod according to the invention will be described.

First of all, as shown in FIG. 12A, an amorphous semiconductor film isformed on an insulation surface, and then, the amorphous semiconductorfilm is subjected to an etching to form an island-like semiconductors6001 and 6002. FIG. 12G is a top view of FIG. 12A, and a sectional viewalong the line A—A′ is FIG. 12A. Then, as shown in FIG. 12B, anamorphous semiconductor film 6003 is formed to cover the island-likesemiconductors 6001 and 6002. It is preferred that, immediately beforeforming the film, the film is subjected to rinse with dilutedhydrofluoric acid to remove oxide film from the surface thereof, andthen the amorphous semiconductor film 6003 is formed immediately. FIG.12H is atop view of FIG. 12B, and a sectional view along the line A—A′is FIG. 12B.

Next, as shown in FIG. 12C, by subjecting the amorphous semiconductorfilm 6003 to a patterning processing, a film 6004 of an island-likesemiconductor film A, which covers the island-like semiconductors 6001and 6002, is formed. FIG. 12I is a top view of FIG. 12C, and a sectionalview along the line A—A′ is FIG. 12C. Then, as shown in FIG. 12D, alaser beam is irradiated selectively to the film 6004 of the island-likesemiconductor film A to increase the crystallinity. FIG. 12J is a topview of FIG. 12D, and a sectional view along the line A—A′ is FIG. 12D.

Next, as shown FIG. 12E, the film 6004 of the island-like semiconductorfilm A, which has been increased in crystallinity, is subjected to apatterning to form a film 6008 which will become an island-likesemiconductor film B. FIG. 12K is a top view of FIG. 12E, and asectional view along the line A—A′ is FIG. 12E. Then, as shown FIG. 12F,a TFT, which uses the film 6008 of island-like semiconductor film B asthe active layer, is formed. Although the following particularpreparation processes may vary depending on the configuration of theTFT, typically, the following steps are carried out; i.e., a step inwhich a gate insulating film 6009 is formed so as to come in contactwith the film 6008 of island-like semiconductor film B; a step in whicha gate electrode 6010 is formed on the gate insulating film; a step inwhich impurity areas 6011 and 6012 and channel forming area 6013 areformed in the island 6008; a step in which an interlayer insulating film6014 that covers the gate insulating film 6009, gate electrode 6010 andthe island 6008; and a step in which wirings 6015 and 6016 that areconnected with the impurity areas 6011 and 6012 are formed on interlayerinsulating film 6014. FIG. 12L is a top view of FIG. 12F, and asectional view along the line A—A′ is FIG. 12F.

The thickness semiconductor film in the impurity areas 6011 and 6012 isadapted so as to be thicker than the thickness of the semiconductor filmin channel forming area 6013. Since the sheet resistant of the impurityarea can be reduced, it is preferred to obtain satisfactory transistorcharacteristics.

Example 3

Example 3 includes a process for crystallizing a semiconductor using acatalyst. Only the point, which is different from the Example 1, will bedescribed. When a catalyst element is used, it is preferred to use thetechniques, which are disclosed in Japanese Patent Laid-Open No.7-130652 and in Japanese Patent Laid-Open No. 8-78329.

After forming the amorphous semiconductor film using Ni, the same issubjected to a solid-phase crystallization (hereinafter, thecrystallization method will be referred to as NiSPC). For example, whenthe technique disclosed in Japanese Patent Laid-Open No. 7-130652, theamorphous semiconductor film is applied with solution of nickel acetatesalt containing Nickel of 10 ppm in weight conversion to form aNickel-containing layer, and after dehydrogenation processing for onehour at 500° C., the same is subjected to a heat treatment for 4-12hours at 500-650° C.; for example, for 8 hours at 550° C., tocrystallize the same. As for applicable catalyst element, in addition toNickel (Ni), an element such as Germanium (Ge), iron (Fe), Palladium(Pd), Tin (Sn), lead (Pb), Cobalt (Co), platinum (Pt), copper (Cu), gold(Au) or the like may be used.

The process of applying the solution of nickel acetate salt and the heattreatment step may be carried out after the island-like semiconductorfilm A has been formed.

By means of laser irradiation method according to the invention, thecrystallinity of the island-like semiconductor film A, which has beencrystallized in a manner of NiSPC, is further increased. Since thepolycrystalline semiconductor obtained by means of laser beamirradiation contains a catalyst element, a process (gettering) to removethe catalyst element from the crystalline semiconductor film is carriedout after the laser crystallization. As for the gettering, thetechniques disclosed in Japanese Patent Laid-Open No. 10-135468,Japanese Patent Laid-Open No. 10-135469 or the like are applicable.

In particular, to a part of the polycrystalline semiconductor, which isobtained after laser irradiation, phosphorous is added and is subjectedto a heat treatment in a nitrogen atmosphere for 5-24 at a temperatureof 550-800° C.; for example, for 12 hours at a temperature of 600° C.When applying the invention, it is preferred that, after adding thephosphorous to the semiconductor area other than island-likesemiconductor film B, which will become the active layer of the TFT inthe island-like semiconductor film A, the heat treatment is carried out.

Owing to this, the area added with the phosphorous in thepolycrystalline semiconductor acts as a gettering site, the phosphorousresides in the polycrystalline semiconductor can be segregated in thearea added with the phosphorous. Owing to this, it is possible to obtainthe island-like semiconductor, in which the density of catalyst elementin the channel area of the TFT has been reduced to less than 1×10¹⁷atoms/cm³, preferably, to approximately 1×10¹⁶ atoms/cm³.

Example 4

In Example 4, a structure of a TFT, which is formed using a laserirradiation method according to the invention, will be described.

A TFT shown in FIG. 13A includes a channel forming area 7001, firstimpurity areas 7002 sandwiching the channel forming area 7001therebetween, and an active layer including second impurity areas 7003sandwiched between the first impurity areas 7002 and the channel formingarea 7001. And further, a gate insulating film 7004 abutting to theactive layer and a gate electrode 7005 formed on the gate insulatingfilm are included in the TFT. Side walls 7006 are formed so as to abutto the side faces of the gate electrode.

The side walls 7006 overlap with the second impurity areas 7003 beinginterposed with the gate insulating film 7004, and the same may beconductive or insulative. When the side walls 7006 are conductive, thesame may be used as the gate electrodes including the side walls 7006.

A TFT shown in FIG. 13B includes a channel forming area 7101, firstimpurity areas 7102 sandwiching the channel forming area 7101, and anactive layer including second impurity areas 7103 sandwiched between thefirst impurity areas 7102 and the channel forming area 7101. Andfurther, a gate insulating film 7104 abutting to the active layer and agate electrode comprised of double-layered conductive films 7105 and7106 built-up on the gate insulating film are included. Side walls 7107is formed so as to abut to the upper surface of the conductive film 7105and to the side surfaces of the conductive film 7106.

The side walls 7107 may be conductive or insulative. When the side walls7107 are conductive, the same may be used as the gate electrodesincluding the side walls 7106.

A TFT shown in FIG. 13C includes a channel forming area 7201, firstimpurity areas 7202 sandwiching the channel forming area 7201, and anactive layer including second impurity areas 7203 formed between thefirst impurity areas 7202 and the channel forming area 7201. Andfurther, a gate insulating film 7204 abutting to the active layer, aconductive film 7205 on the gate insulating film, a conductive film 7206covering the upper surface and the side surfaces of the conductive film7205 and side walls 7207 abutting to the side surfaces of the conductivefilm 7206 are formed. The conductive film 7205 and the conductive film7206 function as the gate electrode.

The side walls 7207 may be conductive or insulative. When the side walls7207 are conductive, the same may be used as the gate electrodesincluding the side walls 7207.

The Example 4 may be carried out in combination with any one of Examples1-3.

As described above, according to the invention, it is possible toprovide a manufacturing method of semiconductor device, which is capableof forming large crystal grains successively by means of artificiallycontrolled super lateral growth, resulting in an increased substrateprocessing efficiency in the laser crystallization process, and which,unlike a conventional SLS method, uses a simple laser irradiation methodwithout requiring a special optical system.

What is claimed is:
 1. A manufacturing method of semiconductor deviceprovided with a thin film transistor over a substrate having aninsulation surface, comprising: forming a non-monocrystal semiconductorover said substrate; forming a marker and an island-like semiconductorlayer A, which is a specific area including an area to become an activelayer of said thin film transistor, in said non-monocrystalsemiconductor in accordance with a layout information of said thin filmtransistor; forming a crystallization area by irradiating a laser beamselectively to said island-like semiconductor layer A using said markeras a positional reference; and etching a periphery area of saidisland-like semiconductor layer A to form an island-like semiconductorlayer B, which becomes an active layer area of said thin filmtransistor, wherein said laser beam is a laser beam of pulseoscillation, and the pulse width of said laser beam of pulse oscillationis 50 ns or more.
 2. A method according to claim 1, wherein said laserbeam uses a solid-state laser oscillator as a light source.
 3. A methodaccording to claim 1, wherein said laser beam uses one or a plurality oflight sources selected from a YAG laser oscillator, a YV0₄ laseroscillator, a YLF laser oscillator, a YAlO₃ laser oscillator, a glasslaser oscillator, a ruby laser oscillator, an alexandrite laseroscillator, a Ti:sapphire laser oscillator, a forsterite laseroscillator or an Nd:YLF laser oscillator.
 4. A method according to claim1, in which said laser beam is a second harmonic, a third harmonic, or afourth harmonic.
 5. A method according to claim 1, in which the beamspot position of said laser beam over the surface of saidnon-monocrystal semiconductor shifts for a distance of 0.3 μm or moreand 5 μm or less at every pulse oscillation.
 6. A method according toclaim 5, wherein the angle, which is formed by the central axis in thelongitudinal direction of said beam spot and the shift direction of saidbeam spot, is orthogonal.
 7. A method according to claim 5, wherein theshift direction of said beam spot resides in the horizontal directionwith respect to the channel length direction of said thin filmtransistor.
 8. A manufacturing method of semiconductor device providedwith a thin film transistor over a substrate having an insulationsurface, comprising: forming a non-monocrystal semiconductor over saidsubstrate; forming a marker and an island-like semiconductor layer A,which is a specific area including an area to become an active layer ofsaid thin film transistor, over said non-monocrystal semiconductor inaccordance with a layout information of said thin film transistor;forming a crystallization area by irradiating a laser beam selectivelyto a specific area including said island-like semiconductor layer Ausing said marker as a positional reference; and etching the peripheryarea of said island-like semiconductor layer A to form an island-likesemiconductor layer B, which becomes an active layer area of said thinfilm transistor, wherein said laser beam is a laser beam of pulseoscillation, and the pulse width of said laser beam of pulse oscillationis 50 ns or more.
 9. A method according to claim 8, wherein said laserbeam uses a solid-state laser oscillator as a light source.
 10. A methodaccording to claim 8, wherein said laser beam uses one or a plurality oflight sources selected from a YAG laser oscillator, a YV0₄ laseroscillator, a YLF laser oscillator, a YAlO₃ laser oscillator, a glasslaser oscillator, a ruby laser oscillator, an alexandrite laseroscillator, a Ti:sapphire laser oscillator, a forsterite laseroscillator or an Nd:YLF laser oscillator.
 11. A method according toclaim 8, in which said laser beam is a second harmonic, a thirdharmonic, or a fourth harmonic.
 12. A method according to claim 8, inwhich the beam spot position of said laser beam over the surface of saidnon-monocrystal semiconductor shifts for a distance of 0.3 μm or moreand 5 μm or less at every pulse oscillation.
 13. A method according toclaim 12, wherein the angle, which is formed by the central axis in thelongitudinal direction of said beam spot and the shift direction of saidbeam spot, is orthogonal.
 14. A method according to claim 12, whereinthe shift direction of said beam spot resides in the horizontaldirection with respect to the channel length direction of said thin filmtransistor.